1. Field of the Invention
The present invention relates to a module adaptable to performing either a brake or clutch function. More particularly the present invention relates to the friction pad assembly of such a module and to the receptacle for holding this pad assembly wherein the receptacle and pad assembly are configured so as to permit the latter to be easily inserted into and removed from the latter. Yet more particularly, the present invention relates to such a pad assembly and receptacle mutually configured so that the pad assembly can be removed/replaced from the receptacle by hand during short down-time periods, without the need to remove any other module components. The present invention relates further to such pad assembly and receptacle wherein the latter is protected against abrasion by the former.
2. Discussion of the Prior Art
The invention described and claimed below provides a continuing improvement in the ease with which the friction pads of various brake and clutch systems can be replaced. It relates to pad-containing modules of a type that can be used, depending on the configuration of the surrounding machinery, to perform either as a brake or as a clutch. These modules are described in a number of earlier patents, including several that are assigned to the assignee of the present invention. For economy of space and time, the pad of the present invention will be described entirely in terms of its being used in a braking module, though it is to be understood that everything that is said about the present invention applies to its use in a clutch module as well. Within the field of braking, the present discussion will for convenience be even more specific, again with no intention of narrowing the understood application of the present invention.
In particular, the pad and pad receptacle of the present invention will be described in the context of their use in web-tension maintenance in those manufacturing procedures in which a series of product modifications is carried out on a continuous webbing of flexible material (xe2x80x9cwebxe2x80x9d) as the web is conveyed along a production line. One example is the production of newsprint. Another is the imprinting of certain types of cloth. In all such operations, it is essential that the tension in the web be maintained above a certain threshold but not so high that it ruptures or otherwise damages the material making up the web. In one configuration, this tension is maintained by placing an adjustable drag on a shaft about which the flexible product is rolled and from which it feeds into the web. This drag can be imposed in a number of ways, but most commonly it involves pressing a brake pad (alternately referred to as a xe2x80x9cbrake shoexe2x80x9d) against a rotor coupled to the shaft; the rotor takes the form of a planar friction plate. By varying the force with which the pad is pressed against the friction plate it is possible to vary the drag and hence to vary (or maintain constant) the tension in the web coming off the shaft. In practice, there will be a number of such pads and the pad pressure on the rotor is effected through the use of an array of pneumatic- or hydraulic-activated brake modules mounted in a fixed diskxe2x80x94a statorxe2x80x94commonly referred to as a xe2x80x9cspider.xe2x80x9d It can be seen also that a clutch can be installed that works in a similarxe2x80x94though, in a sense, opposite,xe2x80x94fashion. That is, the pads will press against the rotor to prevent it from rotating until the web tension rises to a level exceeding the static friction force between the pads and the friction plate, at which point the friction plate will slip and the shaft will continue to rotate until the web tension once falls below sliding-friction force exerted on the friction disk by the pads.
It is advantageous to be able to change the above-described friction pads quickly and easily where they are used in production lines, where time is usually of the essence. For example, it is usually desirable to minimize the production-line down-time associated with removing and/or replacing the pads. A number of patents address the problem of quick pad replacement in brake/clutch modules. Such patents include Baynes et al. (xe2x80x9cDisc Brake with Pocketed Quick Change Shoe Assembly,xe2x80x9d U.S. Pat. No. 3,388,775; 1968), Klaue (xe2x80x9cSpreading Disc Brake with Removable Shoes,xe2x80x9d U.S. Pat. No. 3,885,650; 1975), Montalvo (xe2x80x9cMounting of Cylinders in Friction Brakes and Clutches,xe2x80x9d U.S. Pat. No. 3,964,583; 1976), Yoshida et al. (xe2x80x9cFriction Pad for Disc Brake,xe2x80x9d U.S. Pat. No. 5,890,566; 1999), Demetriou et al. (xe2x80x9cAir Disc Brake,xe2x80x9d U.S. Pat. No. 5,671,827; 1997), Le Deit et al. (xe2x80x9cAssembly Comprising a Friction Pad . . . ,xe2x80x9d U.S. Pat. No. 5,662,191; 1997), Chuang et al. (xe2x80x9cFriction Pad For A Disk Brake,xe2x80x9d U.S. Pat. No. 5,617,935).
Most closely related to the specific nature of the present invention are Montalvo et al. (U.S. Pat. No. 5,178,235; 1993) [hereinafter Montalvo I] and Montalvo et al. (U.S. Pat. No. 5,868,233; 1999) [hereinafter Montalvo II, which is further referenced in application Ser. No. 09/542,639 seeking reissue of Montalvo II]. Both of the last-named patents are assigned to the assignee of the present invention; they describe the particular nature of the modules to which the present invention is directed. They are to be understood to be incorporated into the present discussion.
The spider in which the brake modules are to be mounted is in general a metallic disc thick enough to give it rigidity against the torsional forces exerted on it during the braking process. Distributed around the circumference of the spider, generally equally spaced, are holes, each adapted to receive one of the brake modules. The spider is affixed to a base that is itself floor-mounted. The friction disc (the rotor) is affixed to the roll. Typically, the spider is interposed between the roll and the friction disc. In such a configuration, a shaft coupled to the roll rests on a bushing in the center of the spider, with a portion of the shaft extending to the outboard side of the spider. It is to the outboard end of the shaft that the friction disc is rigidly affixed. The friction disc plane is parallel to that of the spider and both are substantially vertical. Because the brake modules are around the full 360 degrees of the spider, some means must be used to prevent the pad assemblies from falling out of the modules due to gravitational forces.
In addition to gravitational forces, the pad assemblies are exposed to the much greater force resulting from the braking action itself. When the pads are pressed against the rotating friction disc the resulting frictional force tends to carry the pad around with the friction disc. To resist this torsional force xe2x80x9ctorque resistorsxe2x80x9d are placed adjacent to the pad assemblies. In the earlier designs described in the prior art such as Montalvo I, these torque resistors were referred to as xe2x80x9ctorque posts,xe2x80x9d since they were circular in cross-section; the pad assembly had semi-circular openings on its perimeter, one on the distal extremity and a matching one on the proximal extremity, through which torque posts passed when the pad assembly was installed in the module. (As used throughout this discussion, xe2x80x9cdistalxe2x80x9d refers to the direction toward the center of the spider and xe2x80x9cproximalxe2x80x9d refers to the direction away from the center, that is toward the perimeter of the spider. Similarly, with respect to a component, the end of the component intended to be closer to the spider center is the distal end of that component and conversely with respect to its proximal end.) These torque posts prevented the pads from rotating under the torque transmitted to them from the friction plane. They also prevented the pads from moving out radially from the axis of the spider. However, this arrangement required a removal of the proximal post before one could withdraw a pad assembly. Once that post was removed, the pad assembly could be slid along the line between the erstwhile positions of the two torque postsxe2x80x94a line substantially parallel to one of the radii of the spiderxe2x80x94and hence removed from the module. Similarly, the new pad assembly would be slid in along that same line until it fit snugly against the distal torque post, at which point the outer torque post (the proximal post) would be re-installed so as to bind the pad assembly in place. Although simpler than yet earlier designs, this design required considerable time and in general the use of tools to change pads.
As can be seen, the torque posts of Montalvo I also prevented the pad assemblies from falling out under gravity. An additional important role for the torque posts is to guide the installed pad assembly as the pad is pushed forward so as to come into contact with the friction disc.
Subsequent developments, in particular Montalvo II, replaced the posts at the two ends of the pad assembly with torque resistors positioned alongside of the installed pad assembly, where they could continue to hold the assemblies against the forces applied by the friction disc and also to serve as guides at the pad was urged forward toward the friction disc. These new torque resisters were sometimes characterized as xe2x80x9ctorque legsxe2x80x9d rather than posts. They were not circular, but rather elongated in the distal-proximal direction of the brake module, in such a way as to form, in connection with the base from which they protruded, a receptacle into which the pad assembly could be inserted. Although these torque legs resisted torsional forces, they could not prevent the pad assemblies from falling out under gravity. To address that need, Montalvo II taught retainer clips affixed to the outside of the torque legs and extending proximally from those torque legs in such a way that they closed over the proximal ends of a pad assembly once the assembly was in place. These clips were of such a nature that once they had snapped in place, it was necessary to spread them apart in order to extract the pad assembly, and to hold them apart while a new pad assembly was being installed. This at the least required two hands, or some kind of tool arrangement, to change pads.
Another potential problem with the torque resistors of the prior art, whether torque legs or posts, is that they can be eroded by the recurrent forces exerted against them when the pad for which they serve as retainers and guides is pressing against the rotating friction disk. This effect is exacerbated since the object in contact with the torque resistorsxe2x80x94the pad assemblyxe2x80x94includes a hard backing plate to which the pad is affixed. Because of the role it plays, that backing plate is typically made of hard steel. On the other hand, in terms of ease of manufacture and weight considerations, the torque resistors are preferably of a light-weight, easily machined metal such as aluminum. The steel backing plate brought into contact with the torque resistor tends to wear the latter away, requiring a re-furbishing of the brake module during which the torque resistors are replaced. Further, this occurs long before other parts of the modules have to be refurbished.
A final problem with some of the prior art brake modules is the possibility of inserting the friction pad assembly upside down. This can have serious consequences, since this inadvertent inversion results in the hard backing plate rather the friction pad itself being pressed against the rotor during braking. The deleterious consequences range from damaging the surface of the friction disc to the generation of flying fragments, that is, shrapnel.
What is needed therefore is a brake/clutch module that allows for easy one-handed withdrawal and insertion of the associated friction pad assembly. What is further needed is such a module and associated friction pad assembly that do not lead to a reduction in the mean time between repairs below what it is for present brake/clutch modules. What is yet further needed is such a module and associated friction pad assembly so configured that it is not possible to insert the pad assembly upside down. What is desirable is that such a friction pad assembly can be used with much of the installed base of present brake/clutch modules.
An object of the present invention is to provide a brake/clutch module that allows for easier withdrawal and insertion of the associated friction pad assembly than has hitherto been possible. More particularly it is an object of the present invention is to allow for such withdrawal and insertion that can be accomplished by one hand without the need of any tools or removal of parts from the module other than the pad assembly itself. A further object of the present invention is that the modifications it introduces will not adversely affect the mean time between repairs compared with that associated with the modules the invention seeks to replace. A yet further object of the present invention is that it renders impossible the error of inserting the friction pad assembly upside down in the module. It is also an object of the present invention that the new friction pad assembly can be used with some of the already-installed base of modules.
The objects set out above are achieved by a small change in shape of the friction pad assembly and an inversion of the retainer clips from that of Montalvo II. In particular, the retainer clips are deployed so that they grip the pad assembly not at the proximal end but rather at the distal end. Furthermore, the gripping takes place in the device of the present invention in such a way that it is easily overcome by the operator pulling proximally on the pad assembly. In some embodiments of the present invention, the pad is equipped with finger indentations on the sides of the pad near the proximal end, so as to further assist the operator in pulling out the pad assembly. By these changes, it becomes possible for operator to pull the pad assembly out from its receptacle so quickly that there is minimal exposure to high temperatures and hence the procedure can be done (and the pad replaced in the module) in the midst of operation, without waiting for the pad to cool down.
In order to protect the torque legs, which resist the torque imposed by the friction disc and also serve to guide the pad as it is advanced toward the friction disc, the retainer clips of the present invention are further re-configured from the cited earlier design. In the module of the present invention, the retainer clips are caused to run along that side of the torque leg that would otherwise be immediately adjacent to the pad assembly. In other words, they run along the inside of the legs rather than along the outside as was the case with Montalvo II. The spring steel needed to give the retainer clips the strength and resiliency demanded for their releaseably gripping of the pad assembly is much stronger and wear-resistant than the light-weight material (generally aluminum) used for the torque legs and much of the rest of the receptacle. Thus, the clips serve a second purpose, protecting the torque legs against the wear they would otherwise receive from the pad assembly being forced against them by the torsional forces exerted by the friction disc.
The object of making it impossible to insert the pad assembly upside down is achieved in the present invention by a keying addition governing the joinder of the pad assembly and its receptacle. In one embodiment, this involves the addition (a) of a post in the module in a location asymmetric to the module""s center line and (b) a matching concavity in the pad assembly.
As stated previously, for definitiveness, the present invention will discussed in terms of its use with brake modules employed in regulating web tension. However, it can be seen that the present invention has an application wherever a brake or clutch module is used in a context where it is beneficial to be able to quickly and easily change the friction pad. (It is noted, for example, that some of the prior art cited relates to brake assemblies used with automobile and truck brakes.)
The apparatus of the present invention shares with some of the prior art the use of a torque collar which forms the base for torque legs and together with those torque legs forms the receptacle for the friction pad assembly of the present invention. The torque collar, being open in the center, allows a piston to pass through it and against the backing plate of the pad assemblyxe2x80x94the outer reaches of which are resting on the torque collar,xe2x80x94so as to urge the pad assembly forward, bringing the friction pad against the friction disc. There are a variety of mechanical displacement means by which the piston is moved forward so as to force the pad(s) against the disc to be braked. Typically this is done by inflating air bladders behind the pistons. Other devices, including but not limited to hydraulic cylinders and linear motors, may in the alternative be. used to perform this function.
Just as with Montalvo II, retainer clips are used in the device of the present invention to secure the friction pad assembly within the module. In contrast with the prior art, however, these clips are inverted in the sense that the pad-gripping portions of the clips are located at the distal rather than the proximal end of the apparatus. Furthermore, the manner in which the retainer clips of the present invention grips the pad assembly permits smooth withdrawal of the pad assembly with a relatively small force being required to overcome the retainer grip. This contrasts with the cited prior art wherein the retainer clips wrapped around the proximal end of the pad assembly when the latter was in place and had to be separately dealt with (spread apart) as part of the withdrawal and insertion processes. Each retainer clip of the present invention then can be pictured as divided into a portion that is affixed to one of the torque legs (the fixed portion) and a portion that extends distally from the torque leg releaseably snaps onto one side of the pad assembly (the gripping portion). The latter portion of the retainer clip has a shape conforming to an indentation in the side surface of the pad assembly near its proximal end. The rest of each retainer clip is deployed so as to be between a torque leg and the pad assembly when the latter is in place. In some embodiments of the present invention, that portion of the retainer clip wraps completely around the torque leg.
There further developments and refinements to the present invention that will occur to those skilled in the art. These include, but are not limited to, shaping the pad assembly so that it has xe2x80x9cshouldersxe2x80x9d that halt the proximal advance of the assembly once the retainer clips have snapped into place. When there is an indexing post near the proximal end of the pad assembly, as is the case in the Preferred Embodiment, the assembly-halting function of these shoulders is redundant to that of the indexing post. Other features that may be incorporated into the pad assembly of the present invention include shaping the assembly in ways that, while they play no function in the present invention, allow the pad to be used in some of the brake modules of the prior art.